1. Field of Invention
The present invention is related to a polycrystalline silicon film containing Ni which is formed by crystallizing an amorphous silicon layer containing nickel.
2. Discussion of Related Art
In view of performance, low temperature polysilicon, having low production cost owing to its low formation temperature and which also provides a large-scale display area, is as good as high temperature polysilicon.
There are various methods for forming low temperature polysilicon such as solid phase crystallization (SPC), laser crystallization and the like.
In providing low temperature crystallization under 400° C., as disclosed in Hiroyaki Kuriyama, et al., Jpn. J. Appl. Phys. 31, 4550 (1992), the laser crystallization fails to provide uniform crystallization and has difficulty in forming polysilicon on a substrate of a large area due to the need for an expensive apparatus and low productivity.
When polysilicon is formed by solid phase crystallization, uniform crystallites are attained using an inexpensive apparatus. However, solid phase crystallization requires high temperature and long processing time for crystallization, which is inappropriate for a glass substrate due to high production cost.
A new method of crystallizing amorphous silicon at low temperature, called metal induced crystallization, is disclosed in M. S. Haque, et al., J. Appl. Phys. 79, 7529 (1996). Metal induced crystallization crystallizes amorphous silicon by contacting amorphous silicon with a specific kind of metal which induces crystallization of silicon and then subjecting it to annealing. This allows the lowering of the crystallization temperature.
In Ni-induced crystallization, crystallization is accelerated by the NiSi2 which is the final phase of Ni silicide and works as a crystal nucleus, which is disclosed in C. Hayzelden, et al., J. Appl. Phys. 73, 8279 (1993). As a matter of fact, NiSi2, which has a lattice constant of 5.406 Å, similar to that of silicon which is 5.430 Å, also has a structure similar to silicon. Thus, NiSi2 works as a crystal nucleus of amorphous silicon, accelerating crystallization to the direction <111>, which is disclosed in C. Hayzelden, et al., Appl. Phys. Lett. 60, 225 (1992). The crystallization of amorphous silicon is accelerated by metal species.
Metal-induced crystallization is affected by time and temperature of annealing as well as quantity of metal, of which crystallization time is lowered in general when the quantity of metal increases.
Metal induced crystallization has an advantage of low crystallization temperature, which unfortunately requires long thermal process time of over 20 hours at 500° C. Therefore, this method has many difficulties for mass production of polycrystalline silicon.
As the quantity of metal increases, metal induced crystallization becomes more effective. However, the intrinsic characteristics of a silicon film are changed due to metal contamination in the crystallized silicon film.
As mentioned in the above explanation, despite the advantage of low temperature crystallization, metal-induced crystallization has a fatal defect in that the intrinsic characteristics of a silicon film are changed due to metal contamination from the metal used for crystallization which remains in the crystallized silicon film.
Accordingly, the quantity of the metal remaining in the silicon film crystallized by metal-induced crystallization should be optimized to be applied to the current semiconductor device fabrication.